The hepatic uptake and net hepatic clearance of conjugated bilirubin in rats is substantially faster than that of unconjugated bilirubin. An appreciable affinity of conjugated bilirubin for intrahepatic binding proteins, such as ligandin, has been demonstrated. The existence of a significant intrahepatic storage pool for bilirubin monoglucuronide, but not bilirubin diglucuronide, has also been established. These observations may imply that the formation and excretion of bilirubin diglucuronide occurs directly from the canalicular pool of the hepatocyte. Saturable binding of sulfobromophthalein to hepatic canalicular and plasma membranes has been demonstrated. Furthermore, proteins with high affinities for bilirubin and BSP have been isolated from hepatic cell surface membrane fractions suggesting that carrier-mediated transport mechanisms may be of importance in the hepatic uptake and excretion of these organic anions. In studies of bile salt transport it has been shown that microfilaments play a role in hepatic active transport systems and that the excretion of currently unidentified anions contribute to the bile salt independent fraction of bile in the rat.